1. Field of the Invention
The present invention relates to a digital content playback apparatus and a method for editing a digital content, which create new digital content based on license information which defines conditions for permitting edit of a commercial multimedia content.
2. Related Art
In recent years, many DRMs (Digital Right Management) as the technologies that protect copyrights of digital works have been developed. In particular for commercial digital content such as movies or music, due to strong demand for preventing copying of digital content, copyright protection features provide very robust mechanisms and there is no room for users to create and enjoy secondary content for their private use.
In such a situation, international standardization activities are under way, such as ISO/IEC 21000 (MPEG-21) aimed at the distribution and management of various forms of digital content. In MPEG-21, a language (DIDL: Digital Item Declaration Language) for expressing compound content constructed by combination/coupling of a plurality of content parts and a Rights Expression Language (REL) enabling flexible license description are being standardized and a framework for protecting the rights of compound content consisting of a plurality of content parts is being in place. Among reference documents is “Information Technology-Multimedia Framework (MPEG-21)-Part 5: Rights Expression Language, 2004”.
Also in the case of commercial content in an unrewritable medium, provided for next generation DVD players, it is technically possible not only to faithfully play back a pre-prepared content but also to divide the content into components and recombine them to use at the time of playback.
FIG. 12 illustrates an example of an enabling method of the next generation DVDs being studied by AACS (Advanced Access Content System). In medium 101 containing commercial content, the entity of multimedia content consists of content parts referred to as video objects. The video objects are played back or copied as completely integrated content, according to a script called a playlist that controls the timing of executing playback. The playlist is described as a script and is able to control details such as a start time of playback each video object, an order of playback, synchronized playback, display positions on the screen, and so on.
The license conditions (usage rules) of each video object are described in a TUF (Title Usage File). Each video object is encrypted and license conditions of each video object are checked when executing operations such as playback and if the license conditions are satisfied, then it is decrypted using a decryption key and played back according to a playlist.
A player 102 of the medium 101 connects to a server 103 that manages content via networks, and obtains a license of DI_2 recorded in the medium 101, downloads DI_3 to a temporary storage 104 to use it as an work integrated with other video objects originally recorded in the medium, or uses DI_5 provided as steaming integrated with other video objects, and thus more flexible use forms are possible than before. It is also possible to treat sub-content such as subtitles or voice as a kind of video objects. The playlist to use by default is pre-recorded on the medium but it is also possible to request the server 103 to create a new playlist or to permit modification and play back the newly created playlist on the player 102.
The details of the above-mentioned technologies are described in “AACS Introduction and Common Cryptographic Elements Preliminary Draft Revision 0.90, 14 Apr. 2005”.
Permitting a user to generate a new playlist facilitates creating secondary content by combining video objects as content parts or changing the order of playback video object but on the other hand, the copyrights are violated and it will possibly turn into secondary content in which the original intentions of content authors are neglected. This is a major problem in commercial content.
To solve it, for commercial content, an attempt has been started to describe information for limitting modification of a playlist as part of license conditions in a TUF. Using description that extends the above-described Rights Expression Language (REL) allows generic description of rights conditions including basic rights expression. It is proposed in JP-A 2006-099645 (KOKAI) to allow to describe as part of license conditions, a complementary relationship condition specifying an other video object that must be contained together when using the video object in a newly created content.
For commercial content, however, it is expected that users more typically make local modifications by replacing some scenes, music or subtitles to enjoy variations of content than substantial modification the content by using full-fledged video editing tools like nerds. Content holders also desire a mechanism that can not substantially impair the integrity of a work. Playlists also strictly manage the timing of playback each video object, and therefore permitting unknowledgeable users to conveniently replace or rearrange video objects having different playback durations or characteristics may result in content that can not be played back.